CDC Health Alert: Prolonged IgM antibody response in people infected with Zika virus

In July 2016, CDC issued Interim Guidance for Health Care Providers Caring for Pregnant Women with Possible Zika Virus Exposure — United States, July 2016 that includes Zika virus immunoglobulin M (IgM) testing of pregnant women. However, some flavivirus infections can result in prolonged IgM responses (>12 weeks) that make it difficult to determine the timing of infection, especially in testing of asymptomatic people.

Emerging epidemiologic and laboratory data indicate that Zika virus IgM can persist beyond 12 weeks in a subset of infected people. Therefore, detection of IgM may not always indicate a recent infection. Although IgM persistence could affect IgM test interpretation for all infected people, it would have the greatest effect on clinical management of pregnant women with a history of living in or traveling to areas with Zika virus transmission before conception.

Pregnant women who test positive for IgM antibody may have been infected with Zika virus and developed an IgM response before conception.

For asymptomatic pregnant women living in or frequently traveling to areas with Zika virus transmission, Zika virus nucleic acid test (NAT) testing at least once per trimester should be considered, in addition to IgM testing as previously recommended. If positive, this may provide a more definitive diagnosis of recent Zika infection. However, a negative NAT does not rule out recent infection because viral ribonucleic acid (RNA) declines over time.

Other diagnostic methods, such as NAT testing of amniocentesis specimens or serial ultrasounds, may provide additional information to help determine whether the IgM test results suggest a recent infection. Providers should counsel women on the limitations of all tests.

In addition, providers may wish to consider IgM testing as part of pre-conception counseling to establish baseline IgM results before pregnancy; however, preconception negative IgM results might have limited value for women at ongoing risk of Zika infection. For asymptomatic pregnant women living in or frequently traveling to areas with Zika virus transmission with posted CDC Zika Travel Notices, CDC recommends that healthcare providers take these steps:

• Screen pregnant women for risk of Zika exposure and symptoms of Zika. Promptly test pregnant women with NAT if they become symptomatic during their pregnancy or if a sexual partner tests positive for Zika virus infection.
• Consider NAT testing at least once per trimester, unless a previous test has been positive.
• Consider NAT testing of amniocentesis specimens if amniocentesis is performed for other reasons.
• Counsel pregnant women each trimester on the limitations of IgM and NAT testing.

For more information about Zika virus testing, visit www.cdc.gov/zika/pdfs/living_in.pdf.

Visit CDC for the alert and recommendations. https://emergency.cdc.gov/han/han00402.asp.